Int J Clin Exp Med 2016;9(1):260-267 www.ijcem.com /ISSN:1940-5901/IJCEM0015149 Original Article Correlation between morphological abnormalities in the human oocyte, fertilization failure and embryonic development Sen-Lin Shi, Gui-Dong Yao, Hai-Xia Jin, Wen-Yan Song, Fu-Li Zhang, Hong-Yi Yang, Ying-Pu Sun Reproductive Medical Center, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450001, China Received August 27, 2015; Accepted December 10, 2015; Epub January 15, 2016; Published January 30, 2016 Abstract: Objective: The general patient condition, oocyte and embryo condition and clinical outcomes were studied in patients with a morphologically abnormal (ZP). Methods: The general embryo condition was compared between patients with a morphologically abnormal ZP or a normal ZP. The general embryo conditions in the first and subsequent cycles were compared in patients with a morphologically abnormal ZP. Results: Oestradiol (E2) levels were higher in patients with an abnormal ZP than in those with a normal ZP (P<0.05). In the process of promoting ovulation, luteinizing hormone (LH) levels were higher in patients with an abnormal ZP than in those with a normal ZP (P<0.05). The MII rate was significantly lower in patients with a morphologically abnormal ZP than in patients with a normal ZP (P<0.05). After performing intracytoplasmic sperm injection (ICSI), the 2PN fertilization rate and pregnancy rate were significantly lower in patients with a morphologically abnormal ZP than in those with a normal ZP (P<0.05). The gonadotrophin (Gn) dosage for patients with a morphologically abnormal ZP was significantly higher in the second IVF cycle than in the first cycle. The MII rate, 2PN fertilization rate, and pregnancy rate were also significantly higher in the second cycle than in the first cycle (P<0.05). The perivitelline space was smaller within oocytes with a morphologically abnormal ZP than within those with a normal ZP (P<0.05), but the ZP was thicker than normal (P<0.05). Conclusions: Oocytes with a morphologically abnormal ZP had lower maturity, and ICSI can improve the fertilization rate of these oocytes. The application of a modified scheme improved ovum maturation, the fertilization rate, and the pregnancy outcome. Keywords: Zona pellucida morphological abnormality, IVF total fertilization failure, rescue ICSI, PVS, thickness Introduction The fertility rate from conventional in vitro fertilization (IVF) is 60% to 70%. Some patients experience fertilization failure with all oocytes; this incidence is 5% to 20% in the conventional IVF period [1, 2]. Studies have demonstrated that the common reason for total fertilization failure following conventional IVF is that sperm could not penetrate into the cytoplasm through the oocyte (ZP) [3]. The ZP is composed of glycoproteins that are synthesized and secreted by the Golgi apparatus during oocyte generation, and the ZP protects oocytes and fertilized eggs from the outside environment. The ZP of human eggs contains 4 types of glycoproteins, namely, ZP1, ZP2, ZP3, and ZP4 [4]. The ZP, as a sperm barrier, can identify specific substances in the sperm head through receptors on the glycoprotein shell, such as ZP3, which was the first identified receptor. When sperm is encountered, ZP3 induces the sperm acrosome reaction, resulting in ZP penetration and completion of the fertilization process. The structure and function of the ZP play vital roles in signal transmission and material exchange between eggs, embryos, and the internal environment. Therefore, ZP abnormalities may affect oocyte quality and cause fertilization failure and serious problems with embryo quality and potential development. Mannikko [5] reported several single nucleotide polymorphisms (SNPs) in human ZP gene sequences. The loci of the ZP SNPs are associated with the ZP3 genotype and IVF fertilization failure. In laboratory experiments, one type of oocyte with ZP morphological abnormalities
Figure 1. (A and B) Oocytes with morphological abnormalities. (C) A fertilized egg with an abnormal ZP. (D and E) An embryonic abnormal ZP after 48 hours (D) and 72 hours (E). (F and G) Measurements of the perivitelline space in oocytes with a morphologically abnormal (F) or normal (G) ZP. (H and I) Thickness measurements of oocytes with a morphologically abnormal (H) or normal (I) ZP. Scale bar = 50 μm. was conspicuous because the ZP exhibited hyaline changes, serrated changes, pyknosis, lucency, high refraction, even formation of the cytoplasm, a small perivitelline space, and poor maturity. Fertilization of such oocytes usually failed during IVF. Some scholars have studied eggs with a morphologically abnormal ZP and decreased ZP3 protein expression by immunofluorescence staining [6]. Other scholars have examined the ovum ZP using electron microscopy; the results demonstrated that the ZP structure was abnormal [7]. Methods to improve the maturity and fertilization rate of these oocytes with a morphologically abnormal ZP have not been reported. This study analysed the basic condition of the oocytes and embryos in patients with a morphologically normal or abnormal ZP during IVF and compared the patient, oocyte, and embryo conditions of patients with a morphologically abnormal ZP 261 Int J Clin Exp Med 2016;9(1):260-267
between the first and subsequent cycles to explore options for improving oocyte maturation, the fertilization rate, and the pregnancy rate. Data and methods Study participants Between January 2011 and November 2014, 92 patients with complete fertilization failure in the first cycle of IVF, including 28 patients with a morphologically abnormal ZP and 64 patients without an abnormal ZP, were identified at the Reproductive Center of the First Affiliated Hospital of Zhengzhou University. The characteristics of an abnormal oocyte ZP were fewer perivitelline granular cells, a loose structure, and no radioactive shape. The granulosa cells were removed 4 h after IVF, and the oocyte ZP was observed under optical microscopy to assess the presence of hyaline changes, serrated changes, pyknosis, lucency, high refraction, thick ZP, even formation of the cytoplasm, and a small perivitelline space. During intracytoplasmic sperm injection (ICSI), the elasticity of the ZP worsened, the ZP became harder, and the injection points on the ZP were not easy to recover. This type of egg was called a morphologically abnormal oocyte (Figure 1). There were 13 patients with total fertilization failure due to a morphologically abnormal ZP in the first cycle of IVF-assisted reproduction from January 2011 to November 2014. ICSI treatment was then performed in the subsequent cycle. Methods Endocrine determination Venous blood was extracted in the morning of the second or third day of the menstrual cycle. Serum hormones, including oestradiol (E2), progesterone (P), luteinizing hormone (LH), and human chorionic gonadotrophin (hcg), were analysed during the controlled ovarian hyperstimulation (COH) period. Ovulation stimulation control Patients who exhibited complete fertilization failure in the first cycle underwent additional therapy to improve the outcome. A long downregulation protocol of short-acting triptorelin was performed in these patients. After attaining the standards of down-regulation, gonadotrophin (Gn) therapy was initiated. When a type- B ultrasonic instrument showed a follicular diameter of 18 mm in two oocytes, 10000 U of hcg was administered instead of Gn. Oocyte retrieval was performed by transvaginal ultrasound-guided puncture 36 h later. A modified super-long protocol of long-acting triptorelin was performed in patients with a morphologically abnormal ZP in the second cycle. After attaining the standards of down-regulation, human menopausal gonadotrophin (HMG) therapy was initiated. Treatment of oocytes and sperm Oocyte treatment: Follicular fluid was observed under an anatomic lens. Oocyte-granular cell components were identified and then collected. The oocyte-granular cell components were washed with a series of culture media and then incubated in a 6% CO 2 atmosphere at 37 C for 2-3 h. Sperm treatment: Sperm collected through masturbation was liquefied, treated using the density gradient centrifugation method, and stored at 37 C and 6% CO 2 for later use. Observation of embryo condition during insemination and after fertilization Short-term fertilization: Fertilization was performed 39-40 h after hcg injection. Droplet fertilization was performed, and the perivitelline granular cells were removed 4 h after fertilization. The discharge was observed under a microscope. If a second polar body was present in more than 50% of the oocytes, the oocytes were incubated. If a second polar body was present in less than 50% of the oocytes, the oocytes were observed after an additional 2 h. If the second polar body was still only present in less than 50% of the oocytes, rescue ICSI was adopted. ICSI method: Perivitelline granulosa cells were removed 2 h after the egg was removed. Single sperm injection was performed 1-2 h after removal of the perivitelline granulosa cells. The pronucleus condition was observed 16-20 h after fertilization. Embryo cleavage was investigated 48 and 72 h after egg removal. 262 Int J Clin Exp Med 2016;9(1):260-267
Table 1. Comparisons of the general condition and ovulation stimulation outcomes between patients with and without a morphologically abnormal Patients with a morphologically abnormal Patients with a normal Cases (n) 28 64 Age (years) 31.05±4.46 32.07±3.90 0.072 Infertility duration (years) 7.57±4.70 6.58±3.70 0.331 Primary infertility, n (%) 100 (28/28) 71.9 (46/64) 0.002 Secondary infertility, n (%) 0 28.1 (18/64) Basic FSH (IU/L) 7.81±1.77 7.27±1.71 0.184 Basic LH (IU/L) 5.38±3.58 5.12±1.78 0.283 Basic P (nmol/l) 0.49±0.21 0.51±0.26 0.958 Basic E2 (pmol/l) 46.49±16.04 39.96±15.69 0.024 Gn days 11.14±1.80 11.40±1.70 0.989 Gn dose (IU) 2163.10±857.77 2308.99±785.46 0.505 Quantity of >14-mm follicles on hcg injection day (pcs) 8.67±4.45 9.26±3.72 0.518 Peak E2 (pmol/l) 4196.37±2160.89 5029.98±2478.56 0.595 P on hcg injection day (nmol/l) 0.73±0.44 0.97±0.55 0.064 LH on hcg injection day (IU/L) 2.12±0.97 1.72±0.94 0.033 Basic follicular quantity (pcs) 11.10±6.07 11.32±5.37 0.650 Notes: Basic FSH, LH, P and E2 were determinated on the second or third day of the menstrual period; Peak E2, P and LH on hcg injection day were determinated on the hcg injection day. P Perivitelline space and ZP thickness measurements: OCTX software was used to measure the perivitelline space and the ZP thickness under a microscope at 200 magnification (Figure 1). Embryo transfer: Embryo transfer was performed on the second or third day after oocyte retrieval. A maximum of 3 of the best quality embryos were transplanted based on the patient s age and treatment period. Pregnancy diagnosis: A blood hcg level >5 at 14 days after embryo transfer was the biochemical definition of pregnancy. Clinical pregnancy was detected by pregnant bursa and heart tubes on ultrasound 5 weeks after transplantation. Statistical analysis Statistical treatment was performed with SPSS17.0 software. Measurement data were expressed as mean ± standard deviation, and were compared between the two groups with t test. Numeration data were expressed as rate (%), and were compared between the two groups with Chi square test or Fisher-exact probability test. Statistical significance was established at P<0.05. Results Comparisons of the general condition and ovulation stimulation outcomes between patients with and without a morphologically abnormal ZP Among the patients with total fertilization failure, 28 had a morphologically abnormal ZP, and 64 had a normal ZP. The patients with an abnormal ZP had primary infertility. The incidence of primary infertility was higher among patients with an abnormal ZP than among those with a normal ZP. E2 levels were higher in patients with an abnormal ZP than in patients with a normal ZP (P<0.05). During ovulation stimulation of patients with and without an abnormal ZP, there were no obvious differences in the number of follicles, the days or dose of Gn treatment, or the quantity of >14-mm follicles on the hcg injection day. There were no significant differences in the E2 and P levels between the two groups. The LH level was significantly higher in patients with an abnormal ZP than in patients with a normal ZP (P<0.05) (Table 1). 263 Int J Clin Exp Med 2016;9(1):260-267
Table 2. Comparison of semen from the partners of patients with and without a morphologically abnormal Partners of patients with a morphologically abnormal Partners of patients with a normal Sperm density ( 10 6 /ml) 54.39±15.52 52.09±32.83 0.36 Living rate (%) 58.21±16.67 52.33±19.19 0.139 Progressive Motility (%) 37.87±16.13 31.13±14.55 0.140 Sperm deformity rate (%) 41.33±17.05 45.63±18.25 0.146 Notes: Progressive Motility = Grade a sperm + Grade b sperm. (Progressive Motility: Sperm that are swimming from one place to another and not just twitching or going in small circles). Table 3. Comparison of the ICSI results between patients with and without a morphologically abnormal Patients with a morphologically abnormal Comparison of semen from the partners of patients with and without a morphologically abnormal ZP A comparison of the semen from the partners of patients with and without a morphologically abnormal ZP revealed that the sperm density, living rate, forward movement, and sperm deformity rate were not significantly different (Table 2). Comparison of the ICSI results between patients with and without a morphologically abnormal ZP Patients with a normal zona pellucida Required egg quantity (pcs) 7.38±4.99 11.42±5.64 0.001 PVS (μm) 4.94±2.0 13.86±2.13 0.000 Zona pellucida thickness (μm) 14.38±1.13 11.64±1.28 0.000 MII egg quantity (pcs) 4.13±3.59 11.15±5.43 0.000 MII rate (%) 55.9 (99/177) 97.5 (613/629) 0.000 2PN fertilization rate (%) 70.7 (70/99) 82.5 (506/613) 0.005 2PN cleavage rate (%) 88.6 (62/70) 97.0 (491/506) 0.001 3PN fertilization rate (%) 6.1 (6/99) 4.9 (30/613) 0.642 3PN cleavage rate (%) 100 (6/6) 100 (30/30) High-quality embryo rate (%) 58.1 (36/62) 63.5 (312/491) 0.007 Embryo utilization rate (%) 75.8 (47/62) 67.0 (329/491) 0.16 Pregnancy rate (%) 3.6 (1/28) 26.6 (17/64) 0.011 Notes: PVS: perivitelline space; ZP: Zona Pellucida; MII: Metaphase II; 2PN: Two-pronuclear; 3PN: Three-pronuclear. P The number of eggs required, MII egg quantity, and MII rate were significantly lower in patients with a morphologically abnormal ZP than in patients with a normal ZP (P<0.05). After res- tion rate, and pregnancy rate were also significantly higher in the second cycle (P<0.05). E2 levels on the hcg injection day in patients with an abnormal ZP were significantly lower in the second cycle than in the first cycle (P<0.05) (Table 4). Discussion P cue ICSI, the 2PN fertilization rate, cleavage rate, embryo rate, and pregnancy rate were significantly lower in patients with an abnormal ZP than in patients with a normal ZP (P<0.05). Embryo utilization was not significantly different between the two groups. The oocyte perivitelline space was smaller in patients with an abnormal ZP than in patients with a normal ZP (P<0.05). The ZP was thicker in patients with an abnormal ZP than in patients with a normal ZP (P<0.05) (Table 3). Comparison of the patient and embryo conditions in those with a morphologically abnormal ZP in the first and second cycles The Gn dosage in patients with an abnormal ZP was higher in the second cycle than in the first cycle (P<0.05). The MII rate, 2PN fertiliza- In this study, the oocyte ZP with hyaline changes exhibited fertilization failure during shortterm fertilization. After rescue ICSI, the 2PN fertilization rate, cleavage rate, embryo rate, high-quality embryo rate, and pregnancy rate were significantly lower among patients with an abnormal ZP than among those with a normal ZP. The ZP is produced during oocyte growth and reflects the integrity of the follicle and the qual- 264 Int J Clin Exp Med 2016;9(1):260-267
Table 4. Comparison of the patient and embryo conditions between the first and second cycles in patients with a morphologically abnormal First cycle Second cycle P Gn days 11.15±1.82 11.75±2.18 0.377 Gn dose (IU) 1756.73±597.23 2363.54±763.69 0.031 Follicles >14 mm on hcg injection day (pcs) 9.5±4.7 8.1±4.5 0.357 E2 on hcg injection day (pmol/l) 5598.13±2791.00 3745.26±2269.39 0.038 P on hcg injection day (nmol/l) 0.71±0.29 0.54±0.30 0.08 LH on hcg injection day (IU/L) 2.4±1.39 1.71±1.25 0.098 Required egg quantity (pcs) 9.6±6.2 8.0±4.4 0.850 MII quantity (pcs) 3.15±3.08 4.77±3.6 0.115 MII rate (%) 38.7 (41/106) 61.4 (62/101) 0.001 2PN fertilization rate (%) 53.7 (22/41) 82.3 (51/62) 0.002 High-quality embryo quantity (pcs) 0.89±0.93 2.1±2.8 0.116 Pregnancy rate (%) 0 38.5 (5/13) 0.000 Notes: MII: Metaphase II; 2PN: Two-pronuclear. ity of the oocyte. The ZP plays an important role in the sperm-egg union. This study revealed that any ZP glycoprotein abnormality affects the union of sperm and oocyte, the rate of highquality embryo formation, and the embryo cultivation rate [9, 10], causing fertilization failure [8]. ZP protein abnormalities may directly reflect oocyte maturation defects [9]. Therefore, the decreases in oocyte quality and embryo developmental potential are related to the ZP abnormality. Bertrand et al. found that oocytes with a thinner ZP had a higher fertilization rate. Other scholars have proposed that unexplained patient infertility is due to the thickness of the oocyte ZP. In IVF treatment, ZP thickening was the main factor associated with reduced embryo implantation and pregnancy rates, and it affected the hatched blastocyst [10]. In patients with a morphologically abnormal ZP, the ZP was thicker and acted like armour for the embryo, limiting proper embryo development. Even with normal embryos, a good pregnancy rate cannot be obtained. For these patients with an abnormal ZP, hatched blastocysts may increase the embryo implantation rate. In this study, patients with a morphologically abnormal ZP had primary infertility and high baseline levels of E2, which promoted high LH levels. The oocytes in these patients exhibited low maturity, a small perivitelline space, and a thicker ZP, all leading to a low pregnancy rate. The patients with a morphologically abnormal ZP in the first cycle had the same abnormality in subsequent cycles. Changes in the hormonal environment during the egg-laying period and the increase in oestrogen may impact the thickness and hardness of the ZP. These ZP abnormalities may be due to a congenital malformation caused by incorrect fibre connections within the ZP, which have been correlated with oocyte morphology and the degree of maturity. The degree of oocyte maturity was significantly lower in patients with an abnormal ZP than in patients with a normal ZP. An investigation of the ZP maturity process in mice using electron microscopy revealed constant changes in the location, density, and distribution of the glycan connections. These changes also occur in the human oocyte ZP and are hypothesized to be associated with the mature state of the ultrastructure. The relationship between ultrastructural changes in the ZP and oocyte maturity indicates the significance of the regulation of the sperm and ZP union. Oocyte maturity refers to the completion of the first meiotic division. This process is necessary for egg fertilization and embryo development [11]. Scholars previously analysed 30,000 genes from oocytes associated with total fertilization failure using gene chip technology. Meiosis-, cell growth-, and apoptosis-related genes were associated with fertilization failure. Due to the poor maturity of a morphologically abnormal ZP, the question of whether oocyte fertilization failure is associated with meiosis genes needs to be further researched. The modified super-long protocol was applied to study patients with a morphologically abnor- 265 Int J Clin Exp Med 2016;9(1):260-267
mal ZP in subsequent cycles. The LH level decreased, and the oocyte maturation level, fertilization rate, and pregnancy rate were significantly higher than in the first cycle. The improved solutions are generally utilized for patients with endometriosis and adenomyosis, in whom they have improved the quantity and quality of mature oocytes, increased the number of oocytes required, improved the embryo quality, yielded better LH levels on the hcg injection day, stabilized the pregnancy rate, and decreased the spontaneous abortion rate. There have been few reports of these effects in patients with endometriosis and adenomyosis. In patients with an abnormal ZP, the modified super-long protocol was applied in the second cycle, which significantly improved the oocyte maturity, fertilization rate, and pregnancy rate. Influencing oocyte quality with the long downregulation protocol was an effective solution for improving patient prognosis [12], and the application of the modified super-long protocol in the subsequent cycle was an effective solution for increasing oocyte maturity and quality. In previous applications of IVF-assisted reproduction, some patients exhibited general fertilization failure, with a 30%-50% risk of recurrent fertilization failure [13] if the fertilization failure was due to abnormal sperm penetration and oocyte penetration failure. ICSI, which was applied in the subsequent cycle, effectively increased the fertilization and clinical pregnancy rates. Fertilization failure associated with oocytes with a morphologically abnormal ZP was remedied by ICSI, and patients with an abnormal ZP in the first cycle underwent ICSI. Both strategies resulted in normal fertilized eggs and cleavage embryos, which indicated that the obstacles associated with the union of sperm and egg are the main reasons for the association between a morphologically abnormal ZP and total fertilization failure. ICSI was an effective approach for producing normal fertilized eggs. In conclusion, oocytes with ZP hyaline changes were less mature and resulted in poor potential embryo development and low pregnancy rates. The improved ovulation schedule increased oocyte maturity and the fertilization and pregnancy rates, and ICSI was effective in patients with an abnormal ZP. However, due to ethical limitations and the limited sample size, this study did not thoroughly investigate ZP ultrastructure and gene expression, which should be investigated in the future. Acknowledgements This study was supported by the Youth Fund of the First Affiliated Hospital of Zhengzhou University and also supported by an operating grant from the National Natural Science Foundation of China (31471404) to Ying-Pu Sun. Disclosure of conflict of interest None. Address correspondence to: Dr. Ying-Pu Sun, Reproductive Medical Center, The First Affiliated Hospital of Zhengzhou University, Zhengzhou 450001, China. E-mail: syp2008@vip.sina.com References [1] Kuczynski W, Dhont M, Grygoruk C, Pietrewicz P, Redzko S and Szamatowicz M. Rescue ICSI of unfertilized oocytes after IVF. Hum Reprod 2002; 17: 2423-2427. [2] Mahutte NG and Arici A. Failed fertilization: is it predictable? Curr Opin Obstet Gynecol 2003; 15: 211-218. [3] Liu DY and Baker HW. Defective sperm-zona pellucida interaction: a major cause of failure of fertilization in clinical in-vitro fertilization. Hum Reprod 2000; 15: 702-708. [4] Lefievre L, Conner SJ, Salpekar A, Olufowobi O, Ashton P, Pavlovic B, Lenton W, Afnan M, Brewis IA, Monk M, Hughes DC and Barratt CL. Four glycoproteins are expressed in the human. Hum Reprod 2004; 19: 1580-1586. [5] Mannikko M, Tormala RM, Tuuri T, Haltia A, Martikainen H, Ala-Kokko L, Tapanainen JS and Lakkakorpi JT. Association between sequence variations in genes encoding human glycoproteins and fertilization failure in IVF. Hum Reprod 2005; 20: 1578-1585. [6] Margalit M, Paz G, Yavetz H, Yogev L, Amit A, Hevlin-Schwartz T, Gupta SK and Kleiman SE. Genetic and physiological study of morphologically abnormal human. Eur J Obstet Gynecol Reprod Biol 2012; 165: 70-76. [7] Sousa M, Teixeira DSJ, Silva J, Cunha M, Viana P, Oliveira E, Sa R, Soares C, Oliveira C and Barros A. Embryological, clinical and ultrastructural study of human oocytes presenting indented. Zygote 2015; 23: 145-157. 266 Int J Clin Exp Med 2016;9(1):260-267
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